More precisely, the invention relates to the inputting of digital values which comprise a string of digits and which are situated in a predetermined range, only some of whose digital values are valid. This may involve in particular frequencies or channels of a standard means of radiocommunication, which is for example mounted on an aircraft, and in particular a radio intended to allow communication between the pilots of the aircraft and operators on the ground.
To do this, the input device generally comprises:                a means of input able to be actuated by an operator, so as to input the digits of a particular digital value;        a means of display for displaying all the digits input; and        a means of validation able to be actuated by an operator, so as to validate a digital value thus displayed.        
On a means of radiocommunication of an aircraft, the means of input is usually embodied in the form of a dual rotary switch (or dual-ring rotary knob). This dual rotary switch is furnished with a rotary ring of large diameter for selecting the integer digits and with a rotary ring of reduced diameter for selecting the decimal digits. However, the use of such a dual rotary switch for inputting radiocommunication frequencies on an aircraft poses, in particular, three types of problems for users:    a) the introduction of new channels generally entails a considerable increase in the number of digits to be input. The use of a dual rotary switch is not suitable in such a case, on account of the time required to find the appropriate frequency (overly large number of rotations);    b) in the presence of poor weather conditions, the vibrations felt in the flight deck of the aircraft make the use of a rotary switch difficult; and    c) the cues transmitted by a ground control center often comprise only the significant digits of the frequency to be input. Now, the pilot must always input all the digits which form the frequency, and hence also the non-significant digits which are not transmitted to him by the control center. This situation may in particular pose a problem of comprehension for the pilot, which problem may be aggravated by the introduction of new radio channels on the aircraft.